And claustrum And substantia innominata Nucleus accumbens Basal Ganglia It is a number of nuclear (grey matter) masses which lie within the cerebral hemisphere. They are corpus striatum; amygdaloid nucleus and claustrum. Its major components are caudate nucleus; putamen and globus pallidus . These structures are involved in the control of posture and movement. They are sometimes referred to anatomically as the corpus striatum but clinically, as basal ganglia. Notice that the function of amygdala is differ. Gross anatomically, the putamen and globus pallidus are called the lentiform or lenticular nucleus. The corpus striatum are connected with thalamus ; subthalamus of diencephalon and substantia nigra of midbrain.

The lentiform nucleus is three- sided, having a convex lateral surface and 2 other surfaces that converge to a medial apex which lies against the genu of the internal capsule. 1- Putamen: It lies lateral to the internal capsule and globus pallidus. It is separated from the globus pallidus by a thin lamina of nerve fibers ( the lateral medullary lamina ). Lateral to it lies a thin sheet of grey matter ( claustrum ) which separates the white matter into 2 layers, the external capsule and the extreme capsule. Lateral to the extreme capsule lies the cortex of the insula ( deep within the lateral fissure of the hemisphere ).

2- Caudate nucleus: It consists of a large head and body and a tapering, curved tail. The head of the caudate is completely separated from the putamen by the internal capsule. Rostrally, it is continuous with the putamen at the anterior limb of the internal capsule. At this level, the most ventral portion of the striatum is the nucleus accumbens which is connected to the limbic system. The head of the caudate nucleus forms a prominent bulge in the lateral wall of the anterior horn of the lateral ventricle.

The tail of the caudate passes posteriorly and follows the curvature of the lateral ventricle then descends into the temporal lobe where it lies in the roof of the inferior horn of lateral ventricle.

3- Globus Pallidus: It lies medial to putamen, separated from it by the lateral medullary lamina. Its medial apex nestles into the lateral concavity of the internal capsule. It consists of 2 division which are separated by a thin sheet of fibers ( the medial medullary lamina ). The medial segment is the smaller one. The putamen and globus pallidus ( lentiform nucleus ) lie lateral to the internal capsule and deep to the cortex of the insula.

4- Substantia Innominata: It refers to the basal part of the rostral forebrain that lies beneath the corpus striatum. It contains several groups of neurons. One of them is the nucleus basalis that project to the cerebral cortex and utilize acetylcholine as their neurotransmitter. These neurons undergo degeneration in Alzheimer’s disease. 5- Claustrum: It is a thin plate of grey matter placed lateral to lentiform nucleus. Its anteroinferior part fuses with the anterior perforated substance and the amygdaloid nucleus.

Connections of the striatum The caudate nucleus and putamen together referred as the striatum. They are the input regions of the corpus striatum. Since the majority of afferents from other parts of the brain end here rather than in the globus pallidus. Striatal afferents: Corticostriatal fibers They originate from the ipsilateral side of the cerebral cortex. Motor regions of the frontal lobe project mainly to the putamem, where the body is represented in an inverted fashion. The putamen , so considered the most motor part of the striatum. More anterior regions of the frontal lobe and other association cortices project mainly to the caudate nucleus. So, it has more associative functions. Corticostriatal fibers are excitatory to striatal neurones and their transmitter is glutamic acid

2- Thalamostriatal projection: Comes from the intralaminar nuclei of the ipsilateral thalamus ( centromedian and parafascicular nuclei ) to caudate nucleus and putamen. 3- Nigrostriatal projection: Originates from the pars compacta of the ipsilateral substantia nigra of the midbrain tegmentum to caudate nucleus and putamen. The neurons of pars compacta contain the dark pigment neuromelanin. Their transmitter is the monoamine dopamine which has both excitatory and inhibitory effects upon striatal neurons.

4- The nucleus accumbens receives its dopaminergic input (afferent ) from the ventral tegmental area which lies medial to the substantia nigra. This projection is the mesostriatal pathway. 5- Other afferent to the striatum include a projection from the brain stem raphe nuclei which utilize serotonin as its transmitter.

Striatal Efferents Striatopallidal fibers Striatonigral fibers From the caudate nucleus and putamen to globus pallidus. Their neurotransmitter is gamma- aminobutyric acid (GABA ). These projections are inhibitory upon pallidal neurons. The cells that project to the medial segment of globus pallidus contain both substance P and dynorphin. The projection to the lateral segment of globus pallidus contains met-enkephalin. Striatonigral fibers From the caudate nucleus and putamen to the pars reticulata of the substantia nigra. The cells that project to it contains both substance P and dynorphin.

+ -- L. segment - + or - M.segment; pars reticulata Also, to pars reticulata

Connections of the Globus Pallidus The medial segment of the globus pallidus is very similar in structure and function to the pars reticulata of the substantia nigra. They are regarded as the output portion of the basal ganglia Pallidal Afferents: They arise from the striatum . Both utilize GABA as transmitter. In addition each contains peptide cotransmitters. Subthalamopallidal projection: It originates from small structure is located beneath the thalamus, lying against the medial surface of the internal capsule. It has the appearance of a biconvex lens in coronal section. They pass laterally through the internal capsule forming the subthalamic fasciculus and terminate in both segments of globus pallidus mainly the medial. They are excitatory to pallidal neurons using glutamic acid as their transmitter. They also, sends fibers to the pars reticulata of the substantia nigra.

Pallidal efferents: The lateral segments projects to the subthalamic nucleus. They pass through the internal capsule in the subthalamic fasciculus. They are inhibitory and use GABA. The medial segment together with the pars reticulata project to the thalamus ( ventral lateral ;ventral anterior and centromedian nuclei ). pallidothalamic fibers: Some fibers pass round the anterior margin of the internal capsule as ansa lenticularis, while others pass through the internal capsule as lenticular fasciculus. The fibers continue to course medially then loop dorsally and laterally as thalamic fasciculus to enter the ventral aspect of the thalamus. The thalamic project fibers are excitatory fibers to the primary motor and supplementary motor cortices

A smaller projection of the medial pallidal efferent fibers passes caudally to terminate in the brain stem tegmentum in the nucleus tegmenti pedunculopontinus which lies at the boundary between midbrain and pons, surrounding the superior cerebellar peduncle. Efferents of the pars reticularis of the substantia nigra pass to the ventral lateral thalamus to superior colliculus and to brain stem reticular formation including the pedunculopontine nucleus. The nigral cells control the axial musculature including the extraocular muscles.

Function of the Basal Ganglia The basal ganglia are referred as extrapyramidal motor system. Their function is to facilitate purposeful behaviour and movements and to inhibit unwanted or inappropriate (not suitable ) movements. When a movement is initiated from the cerebral cortex, impulses discharge not only through corticospinal and corticobulbar pathways but also through the corticostriatal projection to the neostriatum. These glutamatergic fibers cause excitation of striatal neurons. The first route ( direct pathway ) induce the inhibition of medial pallidal ( for limb movements ) or pars reticulata neurons ( for eye movements ). These output neurons are inhibitory and lead to disinhibition ( loss inhibition ) of the motor thalamus. The resulting increase in the activity of the thalamic neurons causes excitation of the cells of cerebral cortex. The direct pathway facilitate purposeful behaviour and ongoing movement. + _ Or pars reticulata of the substantia nigra The indirect pathway is via the subthalamic nucleus. Efferent from striatum inhibits lateral plallidal neurons which becomes disinhibited to subthalamus causes activation of medial pallidal and nigral neurons and inhibition of thalamus and cortical cells. This pathway has the effect of inhibiting unwanted movements.

1- Huntington’s Disease It is an degenerative autosomal dominant inherited disease with the onset occurring in adult life. Within the striatum, there is progressive ; particular attrition of the cells that project to the lateral segment of the globus pallidus ( indirect segment ). This leads to disinhibition of the lateral pallidal neurons and inhibition of subthalamic nucleus. Medial pallidal neurons , therefore ,become abnormally underactive and unwanted; involuntary movements.The following signs is present: 1- Choreiform movements first appear as involuntary movements of the extremities and twitching of the face (facial grimacing). Later, more muscle groups are involved so the patient becomes immobile and unable to speak or swallow. 2- Progressive dementia occurs with loss of memory and intellectual capacity There is degeneration of the GABA; P-secreting and acetylcholine-secreting.

2- Parkinson’s disease It is a neurodegenerative disease of elderly, of unknown cause. It is characterized by akinesia, flexed posture, rigidity and a resting tremor. It is due to depletion of striatal dopamine levels. It is treated by levodopa which restores normal striatal function. When drug therapy fails, neurosurgical ablation or electrical stimulation of the subthalamic nucleu or medial segment of the globus pallidus can help the patient.

5- Hemiballism 3- Sydenham’s Chorea ( St Vitus’ dance ) The patient exhibits involuntary, quick, jerky, spasmodic, irregular movements that are nonrepetitive. Sudden movements of the head; trunk or limbs. It is a common manifestation of rheumatic fever. 4- Hepatolenticular degeneration (Wilson’s disease) It is an inherited disorder ( autosomal recessive ) of copper metabolism. 5- Hemiballism It is rare with choreiform movements of the limbs on one side of the body. It caused by a lesion of cerebrovascular origin of the contralateral subthalamic nucleus.